Disilane addition versus silane-hydrogen flow rate effect on the PECVD of silicon thin films

Abstract

The effect of small disilane addition to the silane/hydrogen mixture and of the total silane/hydrogen flow rate on the silicon thin film growth rate and crystallinity were investigated. The study was performed by using simplified gas phase chemistry model along with plasma diagnostics such as electrical and deposition rate measurements. The results showed that even small disilane addition induces an increase in the electron density, silane electron-induced dissociation rate, and film growth rate. The increase in the total flow rate caused a linear increase in the film growth rate despite the negligible effect on the discharge microscopic parameters. Similar deposition rates and crystallinities were achieved with both disilane addition and increase in the flow rate, but the deposition efficiency was much higher in the case of disilane addition. The simplified gas phase chemistry model indicated an increase in the silyl production rate either with the disilane addition or the increase in the flow rate. Almost the same silyl production rates were calculated for both parameters, but for the disilane addition case, this was achieved with much less silicon containing molecules in the gas feed. Finally, the increase in the silyl production rate combined to the almost constant hydrogen atoms production, and consumption rate is estimated as the main reason for the drop in the crystallinity with the increase in disilane fraction in the mixture or the total flow rate.